Kinetics of oxidation of hydrogen peroxide by dioxo-bridged manganese(III,IV) complexes

Abstract

The dioxo-bridged manganese(III,IV) complexes [L₂Mn^III(µ-O)₂Mn^IVL₂]³⁺ [L = 2,2′-bipyridine (bipy) 1 or 1,10-phenanthroline (phen) 2] quantitatively oxidised H₂O₂ to O₂, and were themselves reduced to Mn^II. The bipy complex follows biphasic kinetics but the phen complex follows a single exponential profile. For 1, the mononuclear complex [Mn(bipy)₂(H₂O)(OH)]²⁺ is the intermediate, which is a solvolysis product of 1⁺, generated by two-electron reduction of 1³⁺ by hydrogen peroxide. The reaction rate increased with increasing [H⁺] and decreasing [L]. The aqua derivatives of 1 and 2 have greater kinetic activities than their respective parents. The reactions follow an inner-sphere mechanism though all other redox reactions studied so far for 1 and 2 proceed via an outer-sphere model.